The observation of mtDNA translation defects with biochemical evidence of isolated complex IV deficiency is similar to other mitochondrial translation disorders (e.g., RARS2 and YARS2 deficiency) where biochemical findings ranged from normal to multiple RCE defects or isolated complex IV deficiency [20, 21]. Here, YARS2 is linked to hyperinsulinemic hypoglycemia, familial, 4.